Many high performance semiconductor chips and low power semiconductor chips employ local voltage islands that employ a reduced power supply voltage compared to the rest of a semiconductor chip. FIG. 1 shows a prior art semiconductor chip 100 that employs a regular supply voltage region 11, a first local voltage island 12A, and a second local voltage island 12B. Within each of the local voltage islands (12A, 12B), a local power supply voltage, which is lower than the power supply voltage employed in the regular supply voltage region 11, is provided to the semiconductor circuitry therein. As an illustrative example, circuits in the regular supply voltage region 11 may employ 1.5 V, circuits in the first local voltage island may employ 1.2 V, and circuits in the second local voltage island may employ 1.1 V for operation.
Local voltage islands enable energy efficient operation of a semiconductor chip, which becomes critical, for example, in low power semiconductor chips employed in mobile devices operating on a battery. Further, reduction of heat generation from the local voltage islands may enable faster operation of the rest of the semiconductor chip since the operation of the overall semiconductor chip is limited by the total amount of heat generation. For example, the regular supply voltage region 11 of FIG. 1 may be allowed to operate faster and generate more heat if the heat generation from the local voltage islands (12A, 12B) may be reduced.
The local voltage islands (12A, 12B) are designed for a reduced voltage operation. The magnitude of the reduced voltage is determined by the circuit design, and the physical semiconductor chip provides such reduced voltages over a single distribution network or multiple distribution networks to conserve power during operation of the semiconductor chip in a low power mode.
Due to process variations inherent in the manufacture of semiconductor chips, each semiconductor chip may have different minimum operating voltage even for the same local voltage island. Further, the design point for the local supply voltage within a given local voltage island may turn out to be too optimistic, in which case the full power-savings potential of the local supply voltage within a given local voltage island may turn out to be too pessimistic, in which case the circuit within the local voltage island is not fully functional at a nominal operation voltage, i.e., the semiconductor chip may operate only above the nominal operation voltage at which the local voltage island is provided with a higher voltage than the voltage at the design point.
Yet further, process variations inherent in semiconductor manufacturing steps may introduce performance variations between individual semiconductor chips such that an operational voltage range varies from chip to chip. Such operational voltage range may also vary locally within a semiconductor chip from one voltage island to another voltage island.
In view of the above, there exists a need for a circuit for modulating a local supply voltage to a local voltage island as necessary for functional operation of a logic circuit within the local voltage island.
Further, there exists a need for a circuit for determining the minimum local supply voltage that is required to maintain full functionality of the logic circuit within the local voltage island and methods of operating the same.